FIGS. 13(a)-13(b) and 14(a)-14(b) are diagrams grams explaining a prior art solid-state imaging device presented by Ishihara et al at International Electron Device Meeting, 1983. FIG. 13(a) is a plan view showing a disposition of a diffused region on a semiconductor substrate and FIG. 13(b) is a plan view showing a disposition of a charge transfer electrode and a light shielding film. FIGS. 14(a) and 14(b) are cross sections, respectively, taken along a line XIVa--XIVa and a line XIVb--XIVb of FIG. 13(b). Here, in FIGS. 13(a) and 13(b), a flattening film and a lens layer are omitted.
In the figures, a solid-state imaging device 200 comprises an element part 201 including a plurality of light receiving, i.e. responsive, parts that generate electrical signal charges in response to incident light. The light receiving parts have a generally square configuration in plan and are disposed in two-dimensional array, vertical charge coupled devices (hereinafter referred to as CCD), which are disposed among the respective arrays of the light receiving parts, are designed to transfer charges generated in the respective light receiving parts in the vertical direction, a transfer gate part which is disposed between each above-described light receiving part and the vertical CCD, a lens layer 203 which is disposed on the element part 201 and is formed so that incident light is collected in each region corresponding to each light receiving part, and an optical path length adjusting layer 202 which is disposed between the element part 201 and the lens layer 203 and adjusts the optical path length of light collected by the lens layer 203. More particularly, in the element part 201, a p-type well region is formed in an n-type silicon substrate 1. On the surface of the p-type well region 2, a first n-type semiconductor layer 3 serving as the above-described light receiving part, a second n-type semiconductor layer 4 serving as a channel region of the above-described vertical CCD (hereinafter referred to as n-type CCD channel region) and a low concentration n-type semiconductor region 4a serving as a channel region of the above described transfer gate part (hereinafter referred to as n.sup.- -type TC channel region) are formed. A channel separating region comprising a p-type semiconductor layer 5 is formed around the first n-type semiconductor layer 3 which is the light receiving part.
Further, a CCD gate electrode comprising a first polycrystalline silicon (hereinafter referred to as poly-Si) film 7a and a CCD gate electrode comprising a second poly-Si film 7b are alternatingly disposed along the transfer direction of the vertical CCD via a gate insulating film comprising a silicon oxide film 6 over the CCD channel region 4. Here, a portion over the n.sup.- -type TG channel region 4a of the first poly-Si film 7a is a transfer gate electrode.
In addition, an aluminum film 8 is formed covering the CCD gate electrode and the transfer gate electrode, namely, a portion of the first poly-Si film 7a over the n-type CCD channel region 4 and a portion of the second poly-Si film 7b over the n.sup.- -type TG channel region 4a. Here, this aluminum film 8 is a light shielding film which shields the light incident on the respective channel regions 4 and 4a (hereinafter referred to as Al-light shielding film).
Further, the optical path length adjusting layer 202 is a flattening film 9 comprising a transparent resin, which is formed on the whole surface of the Al-light shielding film 8. The lens layer 203 comprises convex microlenses 10 which are disposed on the respective regions corresponding to the plural light receiving parts 3 on the flattening film 9 and collect incident light A into the respective light receiving parts. Here, the microlens 10 is disposed so that a center thereof is exactly over a center of the light receiving part and, as shown by the alternating long and two short dashed lines of FIG. 13(a), has an elliptical configuration in plan which overhangs the CCD channel regions 4. Therefore, incident light over the regions around the light receiving part 3, namely, the n-type CCD channel region 4, the n-type TG channel region 4a and the p-type channel separating region 5, is introduced into the light receiving part 3.
Incident light A on the light receiving surface of the solid-state imaging device 200 is collected at the light receiving part 3 by the microlens 10. At the same time, incident light on the Al-light shielding film 8 is also collected at the light receiving part 3 by the microlens 10. As a result, each light receiving part 3 has actually a large sensitivity even if the area thereof is small. Further, photo-electrons which are caused by the collected light at the light receiving part 3 are accumulated in the light receiving part 3, are transferred to the CCD channel region 4 through the TG channel region 4a with a predetermined timing and are output to a signal processing device at the latter stage by the CCD transferring operation.
However, in the prior art solid-state imaging device 200, the photo-electrons caused by incident light are also generated in the vicinity of the CCD channel region 4 of the above-described p-type well region 2 and these electrons enter into the CCD channel region 4 and mix with signal charges being transferred, resulting in noise called smear. In other words, a focus f10 of the lens 10 is usually set so as to be situated inside the first n-type semiconductor layer 3 constituting the light receiving part and, since incident light A unfavorably broadens conversely under the focal point, photo-electrons E0 and E1 occur in wide regions, mainly directly under the light receiving part 3, in a deeper portion of the well region 2. For example, as illustrated in FIG. 14(a), a part of the incident light A reaches a portion directly under the channel separating layer 5 and part of the photo-electrons E1 caused by the incident light enter the CCD channel region 4.
Still, such solid-state imaging device including a lens layer on an element part through a transparent insulating layer is also disclosed in Japanese Published Patent Applications Sho 61-64158, Hei 2-103962, Hei 2-280376, Sho 60-145776, Hei 2-65171. Particularly, in a solid-state imaging device described in Japanese Published Patent Applications Sho 61-64158, Hei 2-280376 and Hei 2-65171, which, similar to the above-described prior art solid-state imaging device 200, form a light collecting lens with a transparent film on a semiconductor substrate including a light receiving part and a charge transfer part, the same problem occurs as described above: smear occurs because incident light broadens in a portion under a light receiving part.
Further, in a solid-state imaging device described in Japanese Published Patent Application Sho 60-145776, in order to prevent incident light from dispersing because of a lens action of a passivation film or a layer insulating film of which a portion over a light receiving part is curved concavely, a light collecting lens is disposed over the concave part. In this case, however, incident light collected by a light collecting lens broadens in a portion under the light receiving part of the substrate, resulting in smear as the above-described device.
Further, in a solid-state imaging device described in Japanese Published Patent Application Hei 2-103962, in order to enhance light collecting ability at a light collecting lens part, the light collecting lens part is constructed with a convex lens comprising a material whose refractive index is larger and a concave lens comprising a material whose refractive index is smaller, which is disposed under the convex lens, and light is collected by the respective lenses. In this case, the broadening of incident light is much wider in a portion under a light collecting part of a substrate, thereby aggravating smear as described above.